Diversity of biogenic minerals in low-temperature Si-rich deposits from a newly discovered hydrothermal field on the ultraslow spreading Southwest Indian Ridge

A newly discovered hydrothermal field on the ultraslow spreading Southwest Indian Ridge expands the known ranges of biogenic minerals, microbes, and hydrothermal deposits. The deposits from this vent site show typical characteristics of low-temperature hydrothermal deposits. Rare earth element fractionation might be partly influenced by bacterial activity. A physicochemical gradient is present across the layer of deposits, providing suitable microhabitats for various microbes. Molecular phylogenetic analysis demonstrates a diverse range of bacteria, some of which are involved in sulfur, iron, and nitrogen metabolism. A high diversity of biogenic Fe and Si minerals are present in the deposits. Biogenic silica, Fe-sulfides, and Fe-oxides with distinctive morphologies are closely related to microbes. Several novel Fe-oxide structures are found and attributed to new types of biogenic minerals. The precipitation of porous silica spherules and Fe-sulfides can be strongly promoted by extracellular polymer saccharides. Biomineralization features indicate that these deposits evolved through four stages. These results help us to better understand the formation of biogenic minerals and low-temperature deposits associated with microbes in the Earth's modern and ancient seafloor hydrothermal vent fields.